This invention relates to paper feeders provided in image forming apparatus, such as copying machines, facsimile machines and printers.
Japanese Unexamined Patent Publication No. 6-107347 discloses an example of a conventional paper feeder which employs a vacuum paper carrier for holding the uppermost sheet of paper by suction and feeding it to an image-forming section. In this paper feeder, a blower duct in which a lifting nozzle for lifting the uppermost sheet of a stack of paper loaded in a paper bin by blowing air almost horizontally toward an upper-forward end of the stack and a separating nozzle for separating the uppermost sheet from a sheet immediately beneath the uppermost sheet by blowing air obliquely upward toward between the two sheets of paper are provided is located at a lower-front part of the vacuum paper carrier.
On the other hand, Japanese Unexamined Patent Publication No. 10-226426 discloses an image forming apparatus in which a blower blows air against a forward end of upper sheets of paper stacked on a paper tray to lift the uppermost sheet and a paper sucker sucks and transports the uppermost sheet. This image forming apparatus comprises an air-suction-type paper feeder which is constructed such that an upper end portion of a rear paper end aligning plate provided to stand at a rear part of the paper tray is curved or slanted in a paper-feeding direction, and an air flow produced by the blower is reversed by the upper end portion of the rear paper end aligning plate to hold down a rear part of a top surface of the uppermost sheet.
In recent years, recycled paper is widely used in copying machines, for example, from the viewpoint of environmental protection. Among various types of recycled paper, some are apt to develop a problem that cut ends of individual sheets stick together due to inclusion of impurities in raw paper material, for instance. When such types of recycled paper are used, there can arise a problem that even if the paper feeder provided with the blower duct is used as disclosed in Japanese Unexamined Patent Publication No. 6-107347, paper misfeeds or multiple paper sheet feeds would occur due to too low a pressure of air, or too high a pressure of air, blown from the lifting nozzle, respectively.
More specifically, in order to separate and smoothly feed the uppermost sheet of a stack of recycled paper, it is necessary to maintain a properly increased pressure of air blown against the upper-forward end of the stack from the lifting nozzle of the blower duct. If the pressure of blown air is too high, however, sheets immediately beneath the uppermost sheet are likely to lift together with the uppermost sheet and, as a consequence, even if air is blown obliquely upward from the separating nozzle for separating the uppermost sheet, it could not be separated from the sheets beneath it, resulting in an increase in the possibility of multiple paper sheet feeds in which more than one sheet of paper is fed simultaneously.
Especially when the paper has a high electrical resistance and is prone to accumulate electrostatic-charges, the uppermost sheet and one or more sheet of paper beneath it stick together by electrostatic force and these sheets are likely to lift together. This could often cause a multiple paper sheet feed problem in which multiple sheets of paper are sucked and transported at the same time by the vacuum paper carrier.
If the pressure of air blown against the upper-forward end of the stack from the lifting nozzle is set to a low level to prevent the multiple paper sheet feed problem, there could arise such a paper transport problem that the vacuum paper carrier can not attract the uppermost sheet as it can not be separated and lifted from the stack of recycled paper.
In the paper feeder provided with the rear paper end aligning plate disclosed in Japanese Unexamined Patent Publication No. 10-226426, on the other hand, the upper end portion of the rear paper end aligning plate provided to stand at the rear part of the paper tray is curved or slanted in the paper-feeding direction to allow a stream of air blown by the blower against an upper-forward end of a stack of paper to flow up to a rear end of the paper, and the air flow is reversed along the curved or slanted upper end portion of the rear paper end aligning plate to hold down the rear part of the top surface of the uppermost sheet. This construction has an advantage that the uppermost sheet can be easily separated from sheets immediately beneath it as the blown air is caused to expand between them.
Even if the paper feeder is so constructed as to indirectly hold the rear part of the top surface of the uppermost sheet by the reversed air flow as described above, however, it is impossible to retain the rear part of the sheet in a stable fashion. If the pressure of air blown by the blower against the upper-forward end of the stack of paper is too high, the rear part of upper sheets could flutter due to the stream of air passing between the sheets. This would develop a problem that the sheets of paper are apt to become misaligned, causing oblique paper feeds or folded sheet ends, for instance. If the pressure of air blown by the blower against the upper-forward end of the stack of paper is too low on the contrary, it becomes impossible to properly separate the sheets of paper, causing a multiple paper sheet feed problem in which multiple sheets of paper are attracted by the paper sucker and transported.
It is an object of the present invention to provide a paper feeder which is free from the problems residing in the prior art.
It is another object of the invention to provide a paper feeder which can properly separate and convey the uppermost sheet of paper from sheets stacked beneath it in a paper bin and effectively prevent oblique paper feeds and other paper feed problems caused by fluttering of a rear end of each sheet of paper.
According to an aspect of the invention, a paper feeder comprises a paper separator for lifting upper sheets of paper and separating the uppermost sheet from the sheet immediately beneath it by blowing air against an upper-forward end of a stack of paper loaded in a paper bin, and a vacuum paper carrier for holding the uppermost sheet by suction and carrying it. The paper separator has a lifting nozzle for lifting side ends of the upper sheets by blowing air toward side portions, excluding a central portion, of the stack of paper loaded in the paper bin.
According to another aspect of the invention, a paper feeder in which sheets of paper are separated and fed one after another from a stack of paper comprises a plurality of paper-feed belts arranged at right angles to paper-feeding direction and driven in the paper-feeding direction, the paper-feed belts having air-passing capability, a vacuum paper sucker for sucking a sheet which has come closest to the paper-feed belts and holding the sheet onto the paper-feed belts, and an elastic friction member which is located between the adjacent paper-feed belts and exerts frictional resistance on the sheet sucked onto the paper-feed belts by going into contact with the sheet from its side facing the stack of paper, the frictional resistance acting in a direction opposite to the paper-feeding direction.
According to still another aspect of the invention, a paper feeder comprises a paper separator for lifting upper sheets of paper and separating the lifted uppermost sheet from the sheet immediately beneath it by blowing air against an upper-forward end of a stack of paper loaded in a paper bin, a vacuum paper carrier for holding the uppermost sheet by suction and carrying it, a first paper pusher for pushing down a rear central portion of the uppermost sheet at the top of the stack of paper loaded in the paper bin, and a second paper pusher for pushing down rear left and right portions of the uppermost sheet with a smaller force than the first paper pusher.
According to yet another aspect of the invention, a paper feeder comprises a lifting nozzle for lifting upper sheets of paper from a stack of paper loaded in a paper bin by blowing air against an upper-forward end of the stack of paper, and a vacuum paper carrier for holding the lifted uppermost sheet by suction and carrying it. The lifting nozzle has a narrow opening portion for blowing air toward a narrow area including the uppermost part of the stack of paper loaded in the paper bin and a wide opening portion for blowing air toward a wide area including the uppermost part of the stack of paper.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments/examples with reference to the accompanying drawings.